1. Field of the Invention
The present invention relates to an image forming apparatus for exposing a photosensitive medium to light by way of a mask member.
2. Description of Related Art
An image forming apparatus is known which uses, for example as in U.S. Pat. No. 4,810,614, light transmitting sheets (hereinafter referred to as mask members) having images thereon in black that are obtained by taking out red, green and blue components of a colored original image. With the image forming apparatus, photosensitive recording paper to which color capsules are applied is sequentially exposed to filtered light by way of the three mask members to form an image.
FIG. 4 is a sectional view showing a part of the route transmitted by a mask member in an image forming apparatus of the type which have been proposed so far. A mask member 115R for red, another mask member 115G for green and a further mask member 115B for blue are formed by a laser printer or the like (not shown) and are inserted one by one into an inlet port 126 of the apparatus as shown in FIG. 4.
After the mask member 115R, for red, is inserted, it is transported downwardly to a left end of an endless belt 102 which extends in a horizontal direction. Endless belt 102 is formed from a transparent material and is electrically charged by a charging device (not shown). Thus, the mask member 115R is fixed to the endless belt 102 by force of static electricity and transported in the fixed condition by circulation of the endless belt 102. When the mask member 115R arrives at a predetermined exposure position, circulation of the endless belt 102 is stopped.
A photosensitive recording medium 106 drawn out from a cartridge 104 extends below and parallel to endless belt 102. A microcapsule paper, such as that disclosed in U.S. Pat. No. 4,399,209, may be adopted as the photosensitive recording medium 106. An exposure operation is performed while the photosensitive recording medium 106 and the mask member 115R are stopped opposed to one other at the exposure position. A lamp 108, serving as a light source for the exposure, is disposed above the endless belt 102 and three filters 110R, 110G and 110B for red, green and blue respectively are disposed below the lamp 108 such that they may selectively cover the lamp 108. Thus, the lamp 108 is first covered by the filter 110R for red. Lamp 108 and the filter 110R are integrally moved from a left end to a right end of the endless belt 102. Only the red component of the light from the lamp 108 is passed by the filter 110R and reaches the mask member 115R through the transparent endless belt 102. The red light component passes through the portion of the mask member 115R where there is no image or toner, that is at points that are not black, and is blocked by the black image portion of the mask member 115R. Consequently, the exposed surface of the photosensitive recording medium 106 is sensitized by red light in accordance with an image of the mask member 115R so that a latent image for red is formed thereon. After completion of such processing, the endless belt 102 is circulated to feed the mask member 115R to the right. The mask member 115R is fed out of the exposure position and transported upwardly along a route to the right of the apparatus as shown. The route branches into two routes at a position 114, the two routes leading to first and second buffers 116a and 116b. Mask member 115R is fed into the upper route by a gate 118 provided at the branching position 114 and consequently is stored in the first buffer 116a.
Simultaneous with such storage of the mask member 115R, the mask member 115G, for green, is inserted into the image forming apparatus through the inlet port 126. The mask member 115G is then transported along the same route previously transitted by the mask member 115R until it comes to the exposure position. It is to be noted that the photosensitive recording medium 106 is not transported during this operation. After the mask member 115G is positioned opposite to the photosensitive recording medium 106, the lamp 108 is moved from the left end to the right end of the endless belt 102 while covered by the filter 110G thereby performing an exposure operation with only green light.
After exposure of the photosensitive recording medium 106 with green light, the mask member 115G is transported rightwardly by circulation of the endless belt 102 and fed at the branching location 114 into the lower route by the gate 118 so that it is stored in the second buffer 116b. Simultaneously, the mask member 115B, for blue, is inserted and transported to the exposure position. An exposure operation of the photosensitive recording medium 106 with blue light is performed in a manner similar to that previously performed with red and green light.
Thus, latent images for red, green and blue are formed in an overlapping relationship on the same surface of the photosensitive recording medium 106 by the multiple exposure of the three exposure operations. The exposed portion of the photosensitive recording medium 106 is then transported to a developing station while a new portion of the photosensitive recording medium 106 is drawn out from the cartridge 104 and introduced to the exposure position at which it is opposed to the endless belt 102.
Meanwhile, the mask member 115B is transported rightwardly and introduced into the first buffer 116a by the gate 118. Simultaneously, the mask member 115R, which has been stored in the first buffer 116a, is transported leftwardly to rejoin the route from the inlet port 126 side so that it is again transported to the exposure position thereby reinitialing the exposure sequence. In this manner, the mask members 115 are successively transported to the exposure position while transitting a loop defined by the routes for mask member 115 movement provided in the apparatus. The gate 118 is controlled in accordance with the position of one of the buffers 116a and 116b in which a subsequently required mask member 115 is stored. After a predetermined number of images are formed in the manner described above, the mask members 115 are individually discharged by way of exit 120.
However, the apparatus described above, since the routes followed by the mask members 115 form a loop having many curved portions, is subject to sheet or mask member jamming.
Generally in an apparatus as used and described above, the device for producing the mask members (for example, a laser printer) is often placed on the upper portion of the apparatus. As a result, access to any such sheet jamming cannot be provided at a convenient upper portion of the exposure apparatus, the mask forming device being in the way. Because of this, a construction is commonly employed wherein the portion of the apparatus containing the routes followed by the mask members is constructed as a unit such that the unit can be extracted from the lower portion of the reproduction apparatus in order to allow clearance of such paper jams. Such a construction, however, requires a mechanism for extracting the mask member routing unit, and the balance of the apparatus is lost by the shifting weight when the mask member routing unit is extracted. Consequently, the entire reproduction apparatus becomes unstable, making the user uneasy.